1. Field of the Invention
This invention relates to a miniaturized electron beam projection apparatus which detects the state of an object, such as shape, thereof by irradiating the object with an electron beam.
2. Description of the Prior Art
A scanning electron microscope (SEM) is known as one type of electron beam projection apparatus whose schematic structure is shown in FIG. 1. In an electron optical unit of the apparatus shown in FIG. 1, fixed voltages are applied to the cathode 211, wehnelt 212 and anode 213 so that electrons are emitted from the cathode 211. The electrons emitted from the cathode 211 are adjusted in the traveling axis thereof by alignment coils 220, converged by focussing lens 221 and irradiate a sample in fixed position via a stigma coil 222, deflection coil 223 and objective lens 224. Then the scanning electron microscope detects secondary electrons generated from the sample with secondary electron detector 230. The stigma coil 222 adjusts for astigmatism and the deflection coil controls the direction of the electron beam. Also, the pumping system (not shown) connected to vents 250, 251 is provided in order to create a vacuum inside of the electron optical column.
In the scanning electron microscope, as described above, the internal air of electron optical column is evacuated via vents 250, 251 which produces a high vacuum condition therein. Under such a high vacuum condition, the electrons emitted from cathode 211 are condensed and projected against the sample 100 as an electron beam. When the electron beam thus projected is incident upon the surface of sample as primary electrons, secondary electrons are generated in response and then detected by secondary electron detector 230. From the secondary electrons thus obtained, the surface state of the sample is detected.
Since the scanning electron microscope is constructed as described above, it requires a large-scaled electron optical system having various types of lenses and coils for the electron optical system. Further, a pumping system and a substantial electron optical column are also required in order to maintain a high vacuum condition inside the entire large-scaled electron optical system, so that the cost becomes very high and the whole system becomes very large in size- and complex. Consequently, the use of the apparatus has been limited to research and development due to their large size and high cost.